Research this past year was focused on the molecular characterization or excitatory amino acid receptors. A putative kainic acid receptor which we previously purified from frog brain membranes was characterized. Two dimensional electrofocusing/electrophoresis showed the purified protein to be made up of multiple components with an Mr = 48,000. These are similar based on peptide mapping studies. A polyclonal and several monoclonal antibodies, made against the purified receptor, recognized these polypeptides on immunoblots of SDS gels. The polyclonal antibody and several monoclonal antibodies immunoprecipitated kainic acid binding activity from a solubilized frog brain preparation. Using antibodies to the purified receptor, the immunocytochemical distribution in frog brain was found to be indistinguishable from the receptor distribution obtained with radioligand binding autoradiography. The immunocytochemical labeling was punctate and always associated with neuron fibers and dendritic arborizations. Ultrastructural analysis showed immunoreactivity associated with postsynaptic membrane. However, the predominant labeling was on membranes of unmyelinated fibers. Using probes developed based on protein sequence of the purified kainic acid receptor, several clones were isolated from a frog brain cDNA library. The deduced amino acid sequence from the overlapping isolated clones showed that the cDNA encodes a 48 kD protein of 466 amino acids. A characteristic hydrophobic feature found in ligand gated ion channel subunits was conserved in the 48 kD protein. An AMPA binding protein was solubilized and partially purified from rat brain. The solubilized sites migrated as a single peak with gel filtration with an Mr=425,000 and displayed binding characteristics like those of the membrane associated sites.